A road for a traveling vehicle is divided by a white line or other types of marks into multiple lanes. A vehicle is required to travel within a lane. A vehicle is equipped with an vehicle onboard camera for detecting a lane division (such as a white line, a curbstone, and a center divider) beforehand based on a front image captured by the vehicle onboard camera to give a warning to a driver when the vehicle is to deviate from the lane against intension of the driver.
When a vehicle travels along a lane, a lane division (such as a white line) which is detected on a front of the vehicle passes through the side of the vehicle. Accordingly, there is proposed a technology which analyzes a side image captured from a vehicle to detect a white line or the like existing on the side of the vehicle, instead of detecting a white line or the like based on a front image (Patent Literature 1). Since the white line or the like existing on the side of the vehicle is located close to the vehicle, it is supposed that the white line or the like is detectable with higher positional accuracy in comparison with the white line or the like existing in front of the vehicle.
The inventor of the present application has found the following. The technology for detecting a white line or the like based on analysis of a side image captured from a vehicle may erroneously detect a white line or the like. In this case, it may be difficult to secure sufficient reliability.
An image conventionally used for detecting a white line or the like is a relatively far image in the traveling direction (a front direction) of the vehicle, and the detected white line or the like is located far away from the vehicle. By contrast, a white line or the like contained in a side image is located close to the vehicle. The position of the white line or the like contained in the front image does not widely shift within the image even during high-speed traveling of the vehicle. However, the position of the white line or the like in the side image may shift widely and rapidly. Accordingly, the white line or the like contained in the side image may become difficult to track during traveling of the vehicle. Moreover, a situation that a shadow of the vehicle, a connection of the road surface or the like appears in the side image in parallel with the white line or the like may occur. In this case, tracking of the white line or the like may be difficult, and distinction between the white line or the like and the objects other than the white line or the like may also become difficult. During detection of the white line or the like from the side image, the white line or the like may be lost sight, an object other than the white line may be erroneously detected, and it may be difficult to secure sufficient reliability.